Characterization of signals for a Divertor Tokamak Test facility interferometer/polarimeter system

Area of Science:

• Plasma physics
• Fusion energy research
• Optical diagnostics

Background:

• Laser interferometer/polarimeter systems are vital for measuring plasma density and magnetic fields in magnetically confined fusion.
• These diagnostics aid in evaluating plasma magnetic equilibrium and real-time q-profile estimation for feedback control.

Purpose of the Study:

• To analyze interferometric and polarimetric signals from a multi-chord far-infrared system for the DTT tokamak.
• To investigate the impact of plasma birefringence on interferometric phase shifts.

Main Methods:

• Calculated polarimetric signals using approximate formulas and Mueller formalism.
• Solved the equation for laser beam polarization evolution within the plasma.
• Studied the effect of plasma birefringence on interferometric phase shifts.

Main Results:

• The Mueller formalism accurately accounts for crosstalk between Faraday rotation and Cotton-Mouton effects.
• Plasma birefringence was found to perturb interferometric phase shifts, even with initial linear polarization.

Conclusions:

• Accurate analysis of interferometric and polarimetric signals is essential for fusion plasma diagnostics.
• Understanding plasma birefringence is critical for precise measurements in fusion devices like DTT.